This invention relates to improvements in the electrodeposition of zinc from aqueous alkaline plating baths, and preferably from aqueous alkaline plating baths containing little or no cyanide. More particularly, the improvement relates to a new composition which is particularly suitable as a brightener additive for aqueous alkaline zinc electrodepositing baths containing little or no cyanide.
Considerable attention has been directed to the development of zinc electroplating baths which will produce zinc deposits of improved quality. Research has been devoted to improving the overall brightness, the range of allowable current densities, and the ductility of the zinc coatings. Until recently, most of the successful aqueous alkaline zinc plating baths have contained substantial quantities of sodium cyanide and various brightener compositions to improve the brightness of the zinc deposits.
Within the last few years, efforts have been made to improve the environment by reducing the amount of pollutants discharged to the atmosphere and to streams and rivers. Water pollution from the rinse waters of plating operations has been of concern to electroplaters because the rinse waters from plating operations using baths containing cyanide are quite toxic. Methods have been devised to detoxify these rinse waters, but the efficiency of the methods and the costs of equipment and chemicals have made these methods uneconomical.
Some cyanide-free or substantially cyanide-free alkaline zinc plating baths have been developed and are apparently being utilized. For example, U.S. Pat. No. 3,824,158 describes an aqueous alkaline zinc electroplating bath containing an epihalohydrin quaternary salt of aminated polyepichlorohydrin, and the bath is described as being useful for producing bright lustrous electrodeposits of zinc without requiring any cyanide.
U.S. Pat. No. 3,869,358 describes an aqueous alkaline zinc electroplating bath which contains less than about two ounces per gallon of cyanide and which contains a water soluble reaction product of an amine with an epihalohydrin containing recurring tertiary and/or quaternary amine groups. U.S. Pat. No. 3,849,325 also relates to the deposition of a bright zinc coating from an alkaline zinc electroplating bath which contains little or no cyanide. The brightening agent which is incorporated into the bath is obtained by the reaction of a nitrogen-containing heterocyclic compound such as pyridine, pyrazine, quinoline and derivatives thereof, an acyclic amine having at least two functional groups, formaldehyde and an epihalohydrin or a glycerol halohydrin.